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When using a fog spray to prevent plastic shrinkage cracking during a concrete flatwork placement, aren't you taking a chance that the water-cement ratio at the surface will increase, reducing concrete quality?
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What's the difference between hydrophilic and hydrophobic polyurethane grouts? Whenever I ask anyone, they say that hydrophilic grouts "love water" and hydrophobic grouts "hate water," but this means nothing to me when I'm trying to select a grout for a certain application. When should each be used?
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I'm a distributor of concrete repair materials that are often used in steel manufacturing plants.
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We just had our first experience with slab curling. What causes it and what can be done to avoid it?
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If reinforcing bars have been stored outside and have a coating of rust, how much rust is acceptable?
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Where should we place rebar in a floor that's a slab on grade? I've heard it needs to be near the top. But to increase tensile strength, shouldn't it be near the bottom?
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We have a job calling for shrinkage-compensating concrete.
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I am required to monitor the differences between interior and exterior concrete temperatures on a mass concrete placement. How many thermometers, or thermocouples, are needed to get a reliable measure of the internal temperatures?
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When rebar have been bent but then aren't used, is it permissible to straighten them in the field for use as straight bars in reinforced concrete?
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Specifications for entrained-air content always include a minimum and maximum limit. I know that too little air reduces concrete's resistance to damage caused by freeze-thaw cycles and deicers. But if the air content exceeds the maximum by a percent or two, how does that affect the concrete?
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How do you calculate form pressures if the rate of placement for walls will exceed 10 feet per hour or the lift height for columns will exceed 18 feet?
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In ACI 117-90, "Standard Specifications for Tolerances for Concrete Construction and Materials," what are the tolerances for deflections of concrete slabs placed on metal decking supported by structural steel frames? My client has a problem with excessive deflection.
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We're considering using steel fibers instead of rebar to reinforce a concrete slab on grade. However, we're concerned about the effects of these fibers on floating, restraightening and troweling operations, and on floor flatness. What floor flatnesses are achievable when steel fibers are used in...
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We build a lot of forms for square cross-section columns with 24-inch sides. Depending on the forming details, at least half of the 48-inch-wide sheathing panels have to be cut 24 3/4 inches wide to allow for overlap at the corners. That leaves us with a lot of leftover plywood 23 1/4 inches wide...
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We're working on a project that requires building a secondary containment structure using concrete made with Type K expansive cement. The design compressive strength is 4000 psi, which makes us concerned about the low strength-test results we've been gett
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We know that overlaid plywood forming panels have greater dimensional stability and smoother, more durable forming surfaces than nonoverlaid panels. But what factors should we consider when choosing between medium-density overlaid (MDO) and high-density overlaid (HDO) panels?
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We are a small residential contractor in southern Arkansas, building slab-on-grade monolithic foundations reinforced with steel and welded wire fabric. During the past couple of years we started having trouble with slab settlement and cracks in the concrete, so we started pouring wider and deeper...
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We are placing a 4-inch-thick concrete floor for a 93,000-square-foot department store, but the architect has limited the size of each pour to 2,160 square feet to prevent premature shrinkage cracks. This limitation will severely cut our productivity and increase our costs. How can we convince the...
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What is the rate of expansion and contraction for a concrete slab on grade due to temperature changes, and how much movement can be expected because of temperature change?
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We're placing a concrete slab on metal decking, and the plans require welded wire fabric to be supported by chairs. Because the chairs are likely to be dislodged by workers during placement, we're trying to convince the designer that we can pull the fabric into the correct position with hooks. Does...